Analysis of THz generation through the asymmetry of photoelectron angular distributions

Abstract

We analyze the mechanism of THz generation in a gas medium with intense two-color infrared lasers pulses. The dependence of the amplitude of THz emission on the relative phase between the fundamental color (800 nm) and its second harmonic (400 nm) is shown to be identical to the residual current as well as to the asymmetry of the above-threshold-ionization (ATI) photoelectrons along the left versus the right side of the linear polarization axis of the laser, thus confirming the validity of the semiclassical photocurrent model for the THz emission. We further analyze the even vs odd angular momentum distributions of the ATI electrons. The degree of overlap between the even-parity dominant electrons and the odd-parity dominant electrons within each ATI peak determines the strength of the THz emission, thus favoring the model that THz is generated through free-free transitions in the laser field. A model is also provided to obtain the same phase dependence as the four-wave mixing model.

Terahertz Emisssion from Quantum Interference of Electron Trajectories

“…The QTM predicted S THz (τ ) is consistent with commonly used theoretical models including the continuum-continuum transition in SFA and PC model [16]. And the w(p) also can be cross validated with numerical solving time-dependent Schrödinger equation [18]. The QTM would provide more potential theoretical treatment for the TWG.…”

Multiphoton ionization of atoms in two-color laser field and coherent polarization control of terahertz waves

“…Recently, the THz energy of 31 μJ with cylindrical lens focusing was reached [29]. The mechanism of terahertz radiation in a two-color field was suggested in [30] and later studied in several papers; see, in particular, [31][32][33][34][35][36][37] and references therein.…”

Electron trajectory backanalysis for spectral profile in two-color terahertz generation

“…The trajectory predicted S THz (τ ) is consistent with the experimental results, validating the successes of the trajectory method. And the w( p) can also be cross-validated with numerical solving timedependent Schrödinger equation [25]. However, the trajectory method gives a more straightforward insight into the microscopic mechanism of TWG, and directly connects the TWG and PEMDs [17][18][19][20].…”